Composition, amphoteric polymeric flocculant and use of both

ABSTRACT

A composition is provided which comprises amphoteric polymers comprising, as constituent monomer units, a cationic monomer unit, an anionic monomer unit, and optionally a nonionic monomer unit and having a 0.5% salted viscosity of 10 to 120 mPa·s, wherein said amphoteric polymers comprise a first amphoteric polymer satisfying the following expression (1) and a second amphoteric polymer satisfying the following expression (2) or a third amphoteric polymer satisfying the following expressions (3) and (4):  
     Ca 1 /An 1 ≧1  (1)  
     Ca 2 /An 2 &lt;1  (2)  
     Ca 3 /An 3 ≧1  (3)  
     |(Ca 1 −An 1 )−(Ca 3 −An 3 )|≧1.5  (4)  
     wherein Ca 1  and An 1  respectively represent the total mole number of the cationic monomer units and the total mole number of the anionic monomer units in the first amphoteric polymer on a condition that the total mole number of all the constituent monomer units in the first amphoteric polymer is converted to be 100 mol; on a condition similar to the above, Ca 2  and An 2 , and Ca 3  and An 3 , respectively represent the total mole number of the cationic monomer units and the total mole number of the anionic monomer units in the second and third amphoteric polymers. The composition is excellent in various flocculation and dewatering performances for various types of sludge, in particular, for sludge high in ratio of excess sludge, and can be used for process yield improvement in papermaking process.

TECHNICAL FIELD

[0001] The present invention relates to a composition and an amphotericpolymer flocculant excellent in various flocculation and dewateringproperties such that the composition and flocculant are excellent inflocculability and dewaterability, are high in filterability, and yieldgood flocs. It also relates to their uses for dewatering sludge, forretention aid in papermaking, and for others.

BACKGROUND ART

[0002] Conventionally, cationic polymer flocculants have been used alonefor dewatering treatment of sludge; however, in these years, withincrease in amount of generated sludge and deterioration ofcharacteristics of the sludge, the sludge is not satisfactorily treatedby conventional cationic polymer flocculants because they are stillinsufficient in capacity for treating the sludge, moisture content ofdewatered sludge cake, SS recovery rate, peelability of dewatered sludgecake from filter cloth, or the like; thus there has been a demand forimproving these problems.

[0003] For the purpose of improving these defects of the conventionalcationic polymer flocculants, various amphoteric polymer flocculants andvarious dewatering methods by use thereof have been proposed.

[0004] For example, the following methods have been known: (1) a methodof dewatering sludge in which a specific ionic-equivalent cationic-richamphoteric polymer flocculant is added to an organic sludge that doesnot contain any inorganic sludge but is supplemented with an inorganicflocculant at a pH of 5 to 8 (Japanese Patent Publication (Kokoku) No.5-56199), (2) a method of dewatering sludge in which an acrylate basedcationic polymer flocculant and an amphoteric polymer flocculant areadded in combination to organic sludge having a pH of 5 to 8 (JapanesePatent No. 2933627), (3) a dewatering method in which an inorganicflocculant is added to sludge to adjust the pH to be less than 5 andthen a specific composition of anionic-rich amphoteric polymerflocculant is added (Japanese Patent Publication (Kokoku) No. 6-239),and (4) a treatment method of waste water of organic nature, in which aninorganic flocculant, an anionic polymer flocculant and a cationic-richamphoteric polymer flocculant are successively added to the waste water(Japanese Patent Laid-Open No.6-134213).

[0005] The above described dewatering methods (1) to (4) have theirrespective advantages; however, these methods cannot necessarily be saidto be effective against the tendency for recent waste water to becomehard to be dewatered.

[0006] More specifically, since the COD value after treatment of wastewater has been required to be lowered, proportion of activated sludge tobe treated per the whole waste water has become higher. Namely, thesludge subjected to the dewatering treatment has become higher incontent of excess sludge. Also, in case of waste water resulting frompapermaking, recovery rate of fibrous contents from the waste water isincreased whilst fibrous contents in the sludge are lowered, and thusseveral cases have occurred to which conventional polymer flocculantsand dewatering methods cannot be applied.

[0007] Meanwhile, in papermaking processes, when or after afiller-containing stuff is diluted to a final concentration for feedinginto a papermaking machine, a retention aid is added thereto so that thefiller is prevented from flowing from the papermaking machine towhitewater, thereby improving the process yield.

[0008] As the retention aid, water-soluble high-molecular-weightcationic polymers are usually used, which include, for example, cationicacrylamide based polymers, partially hydrolyzed products thereof,Mannich modification products thereof, and the like. Recently, thefollowing methods have been noticed: a method for improving retention inpaper making process in which a cationic polymer is added to a stuff,and then bentonite is added thereto (Japanese Patent Laid-OpenNo.4-281095) and a method in which an acrylamide based polymer and ananionic aluminum-containing silica sol are added in combination to thestuff (Japanese Patent No. 2945761). The acrylamide based polymer asused above is produced by aqueous solution polymerization or the likewith solid content of monomers being set at 10 to 40% by mass, and thepolymer obtained by the aqueous solution polymerization is usually in aform of highly viscous paste. Accordingly, when used as a retention aid,the polymer paste is diluted with water so as to be used as an aqueoussolution of 0.1 to 0.5% by mass.

[0009] The retention aid is essentially different in timing of additionin the papermaking process and molecular weight of useful polymers frompaper strength agents that are used for the purpose of enhancing bondingstrength between pulp fibers, and accordingly increasing the strength torupture, stretch and the like. More specifically, as for the timing ofaddition, the paper strength agent is added after a sizing reagent suchas aluminum sulfate has been added to the stuff, while the retention aidis required to be added immediately before the stuff is fed to apapermaking machine so that flocs of the pulp slurry may not bedestroyed. As for the molecular weight of useful polymers, the paperstrength agent has a molecular weight of hundreds of thousands, whilethe molecular weight of the retention aid exceeds one million, andotherwise sufficient retention improvement cannot be attained. Becauseof such a high molecular weight, addition amount of the retention aidranges from 0.01 to 0. 05% by mass in relation to the pulp, which is avery small amount compared to that of the strength agent which rangesfrom 0.1 to 0.5% by mass. As can be seen from the above describedcharacteristics, the retention aid is required to have characteristicsclose to those of the flocculants used in the waste water treatment.

[0010] The retention aid is a polymer with a molecular weight exceedingone million as described above, and thus is obtained, afterpolymerization, as a water-containing polymer in a form that is pastyand extremely low in solubility in water, thereby causing a problem suchthat an extremely long time is required to completely dilute it for useas an aqueous solution in the actual papermaking process.

[0011] Furthermore, conventional retention aids are insufficient inretention, and have significant defects on alkaline papermaking. Inthese years, the papermaking process is promoted to change to a closedsystem, and accordingly the recycled water and pulp fibers arecontaminated with large amounts of water-soluble inorganic matters andothers originating from the fillers so that the conventional retentionaids are insufficient in retention.

[0012] The present inventors have made intensive researches for thepurpose of finding out a composition, a polymer flocculant and adewatering method, which are excellent in performance of flocculationand dewatering of various types of sludge, in particular, sludge largein proportion of waste sludge, and also finding out a retention aidexcellent in solubility in water and in retention in the papermakingprocess.

DISCLOSURE OF INVENTION

[0013] As a result of various investigations for the purpose of solvingthe above described problems, the present inventors have completed thepresent invention by finding out that a composition containingamphoteric polymers of two or more types that are different from oneanother in copolymerization ratio of cationic monomer units to anionicmonomer units, is effective.

[0014] Hereinafter, the present invention will be described in detail.

[0015] It should be noted that, in the present specification,(meth)acrylate denotes acrylate or methacrylate, (meth) acrylamidedenotes acrylamide or methacrylamide, and (meth)acrylic acid denotesacrylic acid or methacrylic acid.

[0016] 1. Composition

[0017] The amphoteric polymers constituting the composition of thepresent invention may be any copolymer which contains a cationic monomerunit and an anionic monomer unit as indispensable constituent monomerunits.

[0018] The cationic monomer includes tertiary salts. exemplified byhydrochlorides and sulfates of dialkylaminoalkyl (meth)acrylates such asdimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, anddiethylamino-2-hydroxypropyl (meth)acrylate; quaternary saltsexemplified by alkyl halide adducts such as methyl chloride adducts ofdialkylaminoalkyl (meth)acrylates, and aryl halide adducts such asbenzyl chloride adducts of dialkylaminoalkyl (meth)acrylates; tertiarysalts exemplified by hydrochlorides and sulfates of dialkyl(meth)acrylamides such as N,N-dimethyl (meth)acrylamide; and quaternarysalts exemplified by alkyl halide adducts such as methyl chlorideadducts of dialkyl (meth)acrylamides and aryl halide adducts such asbenzyl chloride adducts of dialkyl (meth) acrylamides.

[0019] The anionic monomer includes (meth) acrylic acid and alkali metalsalts such as sodium salt or ammonium salts of (meth) acrylic acid;maleic acid and the like and alkali metal salts thereof;acrylamidealkylalkane sulfonic acids such as acrylamide-2-methylpropanesulfonic acid and alkali metal salts or ammonium salts thereof; andvinyl sulfonic acid and alkali metal salts or ammonium salt thereof.

[0020] The amphoteric polymers may further contain monomers other thanthe above described monomers, more specifically, nonionic monomers, asrequired. Examples of nonionic monomers include (meth)acrylamide;dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl(meth)acrylate; dialkylaminoalkyl (meth)acrylamides such asdialkylaminopropyl (meth)acrylamides; and styrene, acrylonitrile, vinylacetate, alkyl (meth)acrylates, alkoxyalkyl (meth)acrylates,vinylpyridine, vinylimidazole, allylamines and the like. Among these,(meth)acrylamide is preferable.

[0021] Any of the monomers can be used each alone or in combinationthereof.

[0022] Preferable combinations of monomers in the present inventioninclude: (1) a copolymer comprising a tertiary salt or a quaternary saltof a dialkylaminoalkyl acrylate as the cationic monomer, an acrylic acidsalt as the anionic monomer, and an acrylamide as the nonionic monomer;(2) a copolymer comprising a tertiary salt or a quaternary salt of adialkylaminoalkyl methacrylate as the cationic monomer, an acrylic acidsalt as the anionic monomer, and an acrylamide as the nonionic monomer;and (3) a copolymer comprising a tertiary salt or a quaternary salt of adialkylaminoalkyl methacrylate and a tertiary salt or a quaternary saltof a dialkylaminoalkyl acrylate as the cationic monomers, an acrylicacid salt as the anionic monomer, and an acrylamide as the nonionicmonomer.

[0023] In the present invention, the amphoteric polymers are thepolymers each having a value of 10 to 120 mPa·s in terms of 0.5% saltedviscosity which is an index of molecular weight, and it is preferablethat when the polymers are used as amphoteric polymer flocculantsdescribed later, the value falls in the range of 15 to 90 mPa·s in orderto attain a stable dewatering treatment.

[0024] The “0.5% salted viscosity” referred to in the present inventionmeans a value obtained by dissolving an amphoteric polymer in a 4%sodium chloride aqueous solution to obtain a 0.5 wt % solution of thepolymer, and subjecting it to measurement at 25° C. by use of a B typeviscometer with a rotor No. 1 or 2 at 60 rpm.

[0025] Production methods of the amphoteric polymers are notparticularly restricted, but can adopt general polymerization methods.For example, in case of aqueous solution polymerization, a method can beadopted in which thermal radical polymerization is effected usingpotassium persulfate, ammonium persulfate, 2,2′-azobis(2-amidinopropane)dihydrochloride, a redox polymerization initiator or the like as apolymerization initiator, and a photoradical polymerization based on UVirradiation can also be effected using benzoin type-and acetophenonetype photopolymerization initiators. Further, in case of reversed phaseemulsion polymerization, polymerization may be effected using waterinsoluble initiators such as azobisisobutyronitrile and benzoylperoxide, in addition to an above described polymerization initiator.

[0026] The produced gel polymer is then cut and chopped by methods wellknown in the art. The chopped polymer is dried at a temperatures of theorder of 60 to 150° C. by means of a dryer such as a band dryer, arotary dryer, an far-infrared dryer and a vibration flow dryer, madeinto powdered polymer by means of a grinder or the like, and subjectedto size control.

[0027] The composition of the present invention is a compositioncontaining two or more types of amphoteric polymers differing incopolymerization ratio of cationic monomer units to anionic monomerunits, and specifically comprises a first amphoteric polymer satisfyingthe following expression (1) in combination with a second amphotericpolymer satisfying the following expression (2) or a third amphotericpolymer satisfying the following expressions (3) and (4):

Ca₁/An₁≧1  (1)

Ca₂/An₂<1  (2)

Ca₃/An₃≧1  (3)

|(Ca₁−An₁)−(Ca₃−An₃)|≧1.5  (4)

[0028] wherein Ca₁ and An₁ respectively represent the total mole numberof the cationic monomer units and the total mole number of the anionicmonomer units in the first amphoteric polymer on a condition that thetotal mole number of all the constituent monomer units in the firstamphoteric polymer is converted to be 100 mol; on a condition similar tothe above, Ca₂ and An₂ respectively represent the total mole number ofthe cationic monomer units and the total mole number of the anionicmonomer units in the second amphoteric polymer; and on a conditionsimilar to the above, Ca₃ and An₃ respectively represent the total molenumber of the cationic monomer units and the total mole number of theanionic monomer units in the third amphoteric polymer.

[0029] According to a preferred embodiment of the present invention, thefirst amphoteric polymer which is cationic-rich and the secondamphoteric polymer which is anionic-rich are used in combination asamphoteric polymers. In this case, the first amphoteric polymer ispreferably one in which Ca₁/An₁ is 1.5 to 10.0, and the secondamphoteric polymer is preferably one in which Ca₂/An₂ is 0.5 to 0.9.

[0030] According to another preferred embodiment of the presentinvention, two types of cationic-rich polymers, namely, the firstamphoteric polymer and the third amphoteric polymer, are used incombination; in other words, amphoteric polymers are used incombination, which are respectively large and small in differencebetween the amount of anionic constituent monomer units and the amountof cationic constituent monomer units. In this case, it is preferablethat proportion of nonionic monomer units to all the constituent monomerunits in all the amphoteric polymers of the composition is 60 mol % ormore, that is, the ionic monomer units constitute less than 40 mol % ofthe polymers. In this embodiment, it is preferable that Ca₁/An₁ is 1.2to 40.0 and Ca₃/An₃ is 1.2 to 40.0. It is preferable that|(Ca₁−An₁)−(Ca₃−An₃)|is 1.5 to 40.0. If this value is smaller than 1.5,flocculation performance as contemplated by the present invention cannotbe attained when the composition is used as a flocculant. If theproportion of nonionic monomer units is smaller than 60 mol % inrelation to the total constituent monomer units in the amphotericpolymers in the composition, flocculability is sometimes lowered whenthe composition is used as a flocculant.

[0031] The above described first, second and third amphoteric polymerscan be obtained by copolymerization of cationic monomer units, anionicmonomer units and optionally nonionic monomer units in such a way thatthe above described monomer unit ratios are satisfied.

[0032] The composition of the present invention can be produced bymixing the first amphoteric polymer with the second amphoteric polymeror the third amphoteric polymer. Alternatively, in the below describeddewatering of sludge or papermaking process, each of the components canbe added separately.

[0033] For each of the first, second and third amphoteric polymers,either one type or two or more types can be used in combination, howeverit is convenient and preferable to use one type for each of the abovedescribed first, second and third amphoteric polymers.

[0034] Proportion of each of the amphoteric polymers in the compositioncan be appropriately set according to purposes; when the firstamphoteric polymer and the second amphoteric polymer are used incombination, it is preferable that the first amphoteric polymer is usedin the range of 20 to 60% by mass and the second amphoteric polymer isused in the range of 40 to 80% by mass; and when the first amphotericpolymer and the third amphoteric polymer are used in combination, it ispreferable that the first amphoteric polymers is used in the range of 10to 90% by mass and the third amphoteric polymers is used in the range of90 to 10% by mass.

[0035] 2. Uses

[0036] The composition of the present invention can be applied tovarious uses. Examples of the application include polymer flocculants,and thickeners for use in coating compositions and the like. Examples ofthe polymer flocculants include sludge dewatering agents, agents forpapermaking such as retention aids used in the papermaking process, andthe like.

[0037] The composition obtained in the present invention is useful as apolymer flocculant, in particular, as a sludge dewatering agent and aretention aid. Description will be made below on the sludge dewateringagent and the retention aid.

[0038] 1) Sludge Dewatering Agent and Sludge Dewatering Method

[0039] When the sludge dewatering agent of the present invention(hereinafter, sometimes referred to as an amphoteric polymer flocculant)is used, it may be mixed with additives well known in the art includingsodium hydrogen sulfate, sodium sulfate, sulfamic acid and the like asfar as no adverse effect takes place.

[0040] The sludge dewatering agent-of the present invention can beapplied to various types of sludge such as sludge of organic nature, andmixed sludge including flocculated and sedimented sludge and the likederived from sewage, human waste and general industry waste water suchas food industry, chemical industry, and pulp or papermaking industrysludge.

[0041] Particularly, the sludge dewatering agent of the presentinvention can be preferably applied to sludge small in fibrous content,namely, sludge high in ratio of excess sludge. Specifically, the sludgedewatering agent of the present invention can be preferably applied tosludge of 5 SS % or more in terms of ratio of excess sludge, and morepreferably to sludge of 5 to 80 SS % in terms of ratio of excess sludge.The mode in which the first amphoteric polymer and the second amphotericpolymer are used in combination is suitable for application to sludge of20 SS % or more in terms of ratio of excess sludge, preferably to sludgeof 20 to 80 SS % in terms of ratio of excess sludge. Additionally, themode in which the first amphoteric polymer and the third amphotericpolymer are used in combination is suitable for application to sludge of5 SS % or more in terms of ratio of excess sludge, preferably to sludgeof 5 to 40 SS % in terms of ratio of excess sludge.

[0042] The present dewatering method using the sludge dewatering agentis concretely a method in which a sludge dewatering agent is added tosludge so as to form sludge flocs. The floc formation method can followthe methods well known in the art.

[0043] If necessary, inorganic flocculants, organic cationic compounds,cationic polymer flocculants and anionic polymer flocculants canadditionally be used.

[0044] Examples of the inorganic flocculants include aluminum sulfate,aluminum polychloride, ferric chloride, ferrous sulfate, ironpolysulfate and the like.

[0045] Examples of the organic cationic compounds include polymerpolyamine, polyamidine, cationic surfactants and the like.

[0046] In the case where inorganic flocculants or organic cationiccompounds are added, it is preferable to adjust the pH to be 4 to 8since sludge can be treated effectively.

[0047] As for the pH adjustment method, no particular pH adjustment isneeded when an appropriate pH value is obtained after inorganicflocculants or organic cationic compounds are added; however, when thepH range prescribed in the present invention is not satisfied, an acidor an alkali can be added for adjustment.

[0048] Examples of the acids include hydrochloric acid, sulfuric acid,acetic acid, sulfamic acid and the like. Additionally, examples of suchalkalis include caustic soda, caustic potash, calcium hydroxide, ammoniaand the like.

[0049] Examples of the cationic polymer flocculants include homopolymersof the above described cationic monomers, copolymers of the abovedescribed cationic monomers and nonionic monomers, and the like.

[0050] Examples of the anionic polymer flocculants include homopolymersof the above described anionic monomers, copolymers of the abovedescribed anionic monomers and nonionic monomers, and the like.

[0051] In the present invention, when sludge low in fibrous content,namely, sludge high in ratio of excess sludge is used, it is preferableto use an anionic polymer flocculant as well.

[0052] In this case, as for the method for adding these polymerflocculants to the sludge, they may be added either separately orconcurrently; however, it is preferable to add the amphoteric polymerflocculant after the anionic polymer flocculant has been added becausethe effect of the combined use of these polymer flocculants becomeslargest.

[0053] In the case where the first and second amphoteric polymers areused in combination, the anionic polymer flocculant involved may be acopolymer containing the anionic monomer unit of preferably 30 mol % ormore, more preferably 40 mol % or more in copolymerization ratio.

[0054] In the case where the first and third amphoteric polymers areused in combination, the anionic polymer flocculant involved may be acopolymer containing the anionic monomer unit of preferably 5 mol % ormore in copolymerization ratio.

[0055] In both cases, the combination ratio of the anionic polymerflocculant and amphoteric polymer flocculant is preferably such that thecontent of the anionic polymer flocculant is 1 to 70 mass % and thecontent of the amphoteric flocculant is 99 to 30 mass % in relation tothe total amount of all the polymer flocculants.

[0056] Additionally, it is preferable that flocculants are added tosludge in such a way that the ratio of the total sum of the cationicmonomer units to the total sum of the anionic monomer units in all thepolymer flocculants satisfies the following expression (5).

0.3≦Ca_(all)/An_(all)≦10  (5)

[0057] In the above expression (5), Ca_(all) and An_(all) respectivelyrepresent the total mole number of all the cationic monomer units andthe total mole number of all the anionic monomer units on a conditionthat the sum of the total amount of all the cationic monomer units andthe total amount of all the anionic monomer units, in all the polymerflocculants, is converted to be 100 mol.

[0058] Outside this range, the flocculationability sometimes becomespoor, the required amounts of all the flocculants are extraordinarilyincreased, and the moisture contents of the finally-obtained cakesbecome high.

[0059] In the case where the first amphoteric polymer and the secondamphoteric polymer are used in combination, it is further preferablethat the addition is made so that the above described ratio satisfiesthe following expression (5-1).

0.3≦Ca_(all)/An_(all)≦4.0  (5-1)

[0060] In the above expression (5-1), Ca_(all) and An_(all) are the sameas those in the above expression (5).

[0061] In the case where the first amphoteric polymer and the thirdamphoteric polymer are used in combination, it is further preferablethat the addition is made so that the above described ratio satisfiesthe following expression (5-2).

0.5≦Ca_(all)/An_(all)≦10.0  (5-2)

[0062] In the above expression (5-2), Ca_(all) and An_(all) are the sameas those in the above expression (5).

[0063] Addition amounts of the amphoteric polymer flocculants and otherflocculants, stirring speed, stirring time and the like are recommendedto follow the dewatering conditions employed in the prior art.

[0064] In both cases where the first and second amphoteric polymers areused in combination and where the first and third amphoteric polymersare used in combination, proportion of the amphoteric polymerflocculants is preferably 5 to 500 ppm in relation to the sludge amount,and is 0.05 to 1 mass % in relation to SS. When amphoteric polymerflocculants and other polymer flocculants are used in combination, it ispreferable that the total amount of all the polymer flocculantssatisfies the above described proportion.

[0065] The flocs thus formed are dewatered by procedures well known inthe art to form dewatered cakes.

[0066] Examples of the dewatering machines include a screw pressdewatering machine, a belt press dewatering machine, a filter pressdewatering machine, a screw decanter and the like.

[0067] Additionally, the sludge dewatering agent of the presentinvention can be applied to a dewatering method which uses a vessel forgranulation and concentration having a filtering part.

[0068] Specifically, examples of the dewatering methods include a methodin which an inorganic flocculant is added to sludge, then, either aftera sludge dewatering agent has been further added or together with thesludge dewatering agent, the sludge is introduced into the vessel forgranulation and concentration having the filtering part, the filtrate istaken out from the filtering part while the granulation is madeconcurrently, and the granulated matter is subjected to dewatering bymeans of a dewatering machine.

[0069] 2) Retention Aids and Papermaking Methods

[0070] In the case where the composition of the present invention isused as a retention aid, the amphoteric polymers as raw materials forthe composition are preferably powder. In actual use, the amphotericpolymers as raw materials are dissolved in water, and used as an aqueoussolution of preferably 0.01 to 0.5 mass %, more preferably 0.01 to 0.1mass %.

[0071] As a retention aid, a composition is preferable in which thefirst and second amphoteric polymers are contained in combination.

[0072] The method for using the retention aid can adopt a conventionalmethod in such a way that, for example, the aid is added when the stuffis diluted to the final concentration for charging into the papermakingmachine or added after the dilution.

[0073] Stuffs to which the retention aid is applied include those thathave been used in the usual papermaking process, and usually containpulp and filler, and optionally other additives specifically includingsizing agents, fixers, paper strength agents, colorants and the like.

[0074] Examples of the fillers include clay, kaoline, agalite, talc,calcium carbonate, magnesium carbonate, sulfate of lime, barium sulfate,zinc oxide, titanium oxide and the like. Examples of the sizing agentsinclude acrylic acid-styrene copolymers and the like; examples of thefixers include aluminum sulfate, cationic starch, alkylketene dimer andthe like; and examples of the paper strength agents include starch,cationic or amphoteric polyacrylamide and the like.

[0075] As for the manner in which the retention aid is added, an aqueoussolution of the composition can be added, or an aqueous solution of anamphoteric polymer as a raw material of the composition may be addedfollowed by addition of an aqueous solution of another amphotericpolymer.

[0076] Proportion of the retention aid to be added is preferably 0.05 to0.8 mass %, more preferably 0.05 to 0.5 mass % in relation to the drypulp mass in the stuff.

[0077] It is preferable that the retention aid is added in such a waythat the above described ratio between Ca_(all) and An_(all) satisfiesthe above described expression (5-1).

[0078] The pH value of the stuff after adding the retention aid ismaintained to be preferably 5 to 10, more preferably 5 to 8. Immediatelyafter the addition of the retention aid, the stuff is charged into thepapermaking machine.

EXAMPLES

[0079] Hereinafter, the present invention will be more concretelyexplained with reference to examples and comparative examples.

[0080] In the following examples, the term “parts” means parts by mass.

[0081] The amphoteric polymers and anionic polymer flocculants used inthe individual examples were respectively those in powdered form shownin Tables I-1 and I-2.

[0082] The abbreviations appearing in these tables denote as follows:

[0083] DAC: Methyl chloride quaternary salt of dimethylaminoethylacrylate

[0084] AA: Acrylic acid

[0085] AMD: Acrylamide TABLE I-1 Constituent Amphoteric monomer units0.5% Salted polymer (molar ratio) Ca/An viscosity (mPa · s) CR-1DAC/AA/AMD 8.40 71 (42/5/53) CR-2 DAC/AA/AMD 4.00 70 (60/15/25) CR-3DAC/AA/AMD 6.00 85 (12/2/86) CR-4 DAC/AA/AMD 12.00 60 (60/5/35) AR-1DAC/AA/AMD 0.86 35 (30/35/35) CO-1 DAC/AA/AMD 1.18 45 (33/28/39) CO-2DAC/AA/AMD 1.43 44 (40/28/32) CO-3 DAC/AA/AMD 6.33 80 (19/3/78)

[0086] TABLE I-2 Anionic polymer Constituent monomer 0.5% Saltedflocculant units (molar ratio) viscosity (mPa · s) AN-1 AA 70 (100) AN-2AA/AMD 120 (50/50)

Example I-1

[0087] As amphoteric polymers, 25 parts of CR-1 and 75 parts of AR-1were used and mixed together to produce a composition, which was used asan amphoteric polymer flocculant BL-1 (Table I-3).

[0088] Two hundred milliliters (200 ml) of a mixed sludge, which wascomposed of a scum waste water of a recycled wastepaper pulp waste water(SS: 33,400mg/l, VSS: 16,900 mg/l, fibrous content: 290mg/l) and anexcess sludge (SS: 10,700 mg/l, VSS: 8,200 mg/l, fibrous content: 80mg/l) in a mixing ratio of 55:45 (SS %), was sampled and placed in a 300ml beaker, to which the amphoteric polymer flocculant was added. Then,the sludge was transferred into a 300 ml empty beaker, and this transferwas repeated 5 times in total. Thereafter, the suspension was stirred 50times with a spatula to form flocs, and then flocculationability of theflocs was evaluated on the basis of the below described three grades,and the diameter of the obtained flocs was measured.

[0089] Thereafter, by using a piece of filter cloth of 80 mesh size as afilter, the above described sludge floc suspension was subjected togravitational filtration, and volume of the filtrate after the elapsedtime of 10 seconds was measured, which was taken as the filtration rate.Additionally, self-supportability of the cakes on the piece of filtercloth and appearance of the filtrate were respectively evaluated on thebasis of the below described sets of three grades.

[0090] The obtained cake was sandwiched with punching metals of 4 mmφ, aload of 6.5 kg×3 minutes was loaded, the weight of the cake that hadescaped through the punching holes (punching leak) was weighed, andpeelability of the cake in relation to the piece of filter cloth wasevaluated on the basis of the below described three grades.

[0091] The evaluated results are shown in Table I-4. The sludgedewatering method of Example I-1 was found to be excellent in all theevaluated flocculation performances.

[0092] Flocculationability

[0093] Excellent: On stirring, flocs of large diameter were immediatelyformed.

[0094] Good: After stirring continued for a while, flocs of largegranular diameter were formed.

[0095] Poor: Even after continued stirring, merely flocs of smalldiameter were formed.

[0096] Filtrate Appearance

[0097] Excellent: Completely transparent.

[0098] Good: A slight amount of suspended solid was found.

[0099] Poor: A large amount of suspended solid was found.

[0100] Self-Supportability

[0101] The floc suspension is poured into a cylindrical vessel whensubjected to gravitational filtering, and after filtration thecylindrical vessel is removed, and evaluation was made.

[0102] Excellent: The cake stood completely by itself.

[0103] Good: The cake collapsed slightly.

[0104] Poor: The cake collapsed completely.

[0105] Peelability

[0106] The cake was peeled off from the piece of filter cloth, andcondition of the piece of filter cloth was observed.

[0107] Excellent: Absolutely not stained.

[0108] Good: Slightly stained.

[0109] Poor: Stained.

Examples I-2 to I-5

[0110] As amphoteric polymer flocculants, a flocculant BL-2 was alsoprovided, which was produced in a manner similar to Example I-1 usingamphoteric polymers shown in Table I-3.

[0111] Dewatering treatment of sludge was carried out in the same manneras that in Example I-1, except that an anionic polymer flocculant shownin Table I-4 was added to the sludge, and then an amphoteric polymerflocculant shown in Table I-4 was added thereto.

[0112] The results evaluated in the same manner as in Example I-1 areshown in Table I-4. The sludge dewatering methods of Examples I-2 to I-5were all found to be excellent in all the evaluated flocculationperformances. TABLE I-3 Average ratio mixed between the Amphotericconstituent polymer Amphoteric monomers (molar Ca/An after flocculantpolymers (parts) ratio) mixing BL-1 CR-1 AR-1 DAC/AA/AMD 1.18 (25) (75)(33/28/39) BL-2 CR-2 AR-1 DAC/AA/AMD 1.43 (40) (60) (40/28/32)

[0113] TABLE I-4 Flocculants Anionic Amphoteric Evaluated resultspolymer polymer Floc Punching flocculant flocculant diameter FilteringFiltrate leak Self- Peel- Example (ppm) (ppm) Ca_(all)/An_(all)Flocculationability (mm) rate appearance (g) supportability ability I-10 BL-1 1.18 Good 10-13 145 Good 0.3 Good Excellent (180) I-2 AN-1 BL-10.99 Excellent 10-20 165 Good 0.0 Excellent Excellent (7) (173) I-3 AN-2BL-1 1.01 Excellent 10-15 160 Good 0.0 Excellent Good (11) (169) I-4AN-1 BL-2 1.00 Excellent  8-15 155 Good 0.1 Excellent Good (15) (165)I-5 AN-2 BL-2 1.00 Excellent  5-10 150 Good 0.2 Excellent Good (25)(155)

Comparative Example I-1

[0114] Sludge dewatering treatment was carried out in the same manner asin Example I-1, except that an amphoteric polymer flocculant shown inTable I-5 was applied to the sludge.

[0115] The results evaluated in the same manner as in Example I-1 areshown in Table I-5.

[0116] The ratio between the constituent monomers in the amphotericpolymer flocculant CO-1 used in Comparative Example I-1 was the same asthe ratio after mixing between the constituent monomers in theamphoteric polymer flocculant BL-1 used in Example I-1, but all theevaluated flocculation performances were found to be insufficient.

Comparative Examples I-2 and I-3

[0117] Sludge dewatering treatment was carried out in each ofComparative Examples I-2 and I-3 in the same manner as in Examples I-2to I-5, except that an anionic polymer flocculant and an amphotericpolymer flocculant shown in Table I-5 were applied to the sludge.

[0118] The results evaluated in the same manner as in Example I-1 areshown in Table I-5.

[0119] The ratios between the constituent monomers in the amphotericpolymer flocculants CO-1 and CO-2 respectively used in ComparativeExamples I-2 and I-3 were the same as the ratios after mixing betweenthe constituent monomers in the amphoteric polymer flocculants BL-1 andBL-2 respectively, but all the evaluated flocculation performances werefound to be insufficient. TABLE I-5 Flocculants Anionic AmphotericEvaluated results polymer polymer Floc Punching Comparative flocculantflocculant Ca_(all)/ Flocculation- diameter Filtering Filtrate leakSelf- example (ppm) (ppm) An_(all) ability (mm) rate appearance (g)supportability Peelability I-1 0 CO-1 1.18 Poor 1-2 45 Turbid 4 GoodPoor (180) I-2 AN-1 CO-1 1.00 Poor 1-2 80 Turbid 2 Good Poor (10) (170)I-3 AN-1 CO-2 0.99 Poor 1-2 85 Turbid 3 Good Poor (16) (164)

Example II-1

[0120] As amphoteric polymers, 30 parts of CR-1 and 70 parts of CR-3were used and mixed together to produce a composition, which was used asan amphoteric polymer flocculant BL-3 (Table II-1).

[0121] Two hundred milliliters (200 ml) of a mixed sludge, which wascomposed of a papermaking/pulp waste water (SS: 47,900 mg/l, VSS: 29,000mg/l, fibrous content: 8,500 mg/l) was sampled and placed in a 300 mlbeaker, to which the amphoteric polymer flocculant was added. Then, thesludge was transferred into an empty 300 ml beaker, and this transferwas repeated 5 times in total. Thereafter, the suspension was stirred 50times with a spatula to form flocs, and then flocculationability of theflocs was evaluated on the basis of the three grades in the same manneras in Example I-1, and the diameter of the obtained flocs was evaluatedafter the prescribed times of stirring.

[0122] Thereafter, by using a piece of filter cloth of 80 mesh size as afilter, the above described sludge floc suspension was subjected togravitational filtration, and volume of the filtrate after the elapsedtime of 10 seconds was measured, which was taken as the filtration rate.Additionally, self-supportability of the cakes on the piece of filtercloth, appearance of the filtrate, and peelability of the cake inrelation to the piece of filter cloth were respectively evaluated on thebasis of the sets of three grades in the same manner as in Example I-1.

[0123] The moisture content of the cake was obtained as follows: theobtained sludge flocs were placed on a piece of filter cloth andsubjected to 3 stages of squeezing by means of a mini belt machine witha running speed of 0.5 m/min and a pressure of 0.5 kg/cm²; then, thecake was heated at 105° C. for 12 hours, and the weight decrement of thecake thus obtained yielded the water content.

[0124] The evaluated results are shown in Table II-2. The sludgedewartering method of Example II-1 was found to be excellent in all theevaluated flocculation performances. TABLE II-1 Average ratio betweenthe Nonionic mixed monomer/ Amphoteric Amphoteric constitutent all Ca/Anpolymer polymers monomers monomers after flocculant (parts) (molarratio) (Ca₁ − An₁) − (Ca₂ − An₂) (mol %) mixing BL-3 CR-1 CR-3DAC/AA/AMD 27 78 6.3 (30) (70) (19/3/78)

[0125] TABLE II-2 Flocculants Evaluated results Amphoteric Floc Moistureflocculant Ca_(all/) diameter Filtering Filtrate content Self- Example(ppm) An_(all) Flocculationability (mm) rate appearance (%)supportability Peelability II-1 BL-3 6.33 Good 3-5 90 Good 61.1 GoodGood (60)

Comparative Example II-1

[0126] Sludge dewatering treatment was carried out in the same manner asin Example II-1, except that an amphoteric polymer flocculant shown inTable II-3 was applied to the sludge.

[0127] The results evaluated in the same manner as in Example II-1 areshown in Table II-3.

[0128] The ratio between the constituent monomers in the amphotericpolymer flocculant CO-3 used in Comparative Example II-1was the same asthe ratio after mixing between the constituent monomers in theamphoteric polymer flocculant BL-3 used in Example II-1, but all theevaluated flocculation performances were found to be insufficient. TABLEII-3 Flocculants Evaluated results Amphoteric Floc Moisture Comparativeflocculant Ca_(all/) diameter Filtering Filtrate content Self- example(ppm) An_(all) Flocculationability (mm) rate appearance (%)supportability Peelability II-1 CO-3 6.33 Poor 1-2 50 Turbid 63.1 GoodPoor (60)

Examples III-1 and III-2

[0129] As a retention aid, an aqueous solution containing 0.05 mass % ofa mixture composed of 70 parts of CR-1 and 30 parts of AR-1 was used.The retention aid was produced as follows: CR-1 and AR-1 were added towater under stirring, dissolved in 30 minutes after addition, andstirred further for 30 minutes. This is referred to as the retention aidBL-4 (Table III-1).

[0130] An aqueous solution containing 0.05 mass % of a mixture composedof 60 parts of CR-4 and 40 parts of AR-1 was produced in the same manneras described above. This is referred to as the retention aid BL-5 (TableIII-1).

[0131] A 1 mass % pulp slurry of CSF=450 ml was prepared bydisintegrating and beating LBKP sheets; while stirring at 1,000 rpm, thefollowing components (1) to (5) were successively added to the slurry inthe order of description, and the total retention was measured by meansof the dynamic drainage jar method. The results obtained are shown inTable III-2. The final pH value of the pulp slurry was 7.2.

[0132] (1) Light calcium carbonate: 20 mass % (a proportion in relationto the pulp solid content in the pulp slurry, and hereinafter referredto as “in relation to pulp”)

[0133] (2) Cationic starch: 0.3 mass % (in relation to pulp)

[0134] (3) Aluminum sulfate: 1.7 mass % (in relation to pulp)

[0135] (4) Paper strength agent (a 15 mass % aqueous solution of acopolymer made of DAC/AA/AM=20/10/70 (molar ratio) Viscosity: 3,500mpa·s): 0.5 mass % (in relation to pulp)

[0136] (5) Retention-aid: 250 ppm (solid content, in relation to pulp)

Example III-3

[0137] Performances of a retention aid were evaluated in the same manneras in Example III-1, except that as the retention aid, a 0.05 mass %aqueous solution of the amphoteric polymer AR-1 was added in 70 ppm(solid content, in relation to pulp), and then 0. 05 mass % aqueoussolution of the amphoteric polymer CR-1 was added in 175 ppm (solidcontent, in relation to pulp). The results obtained are shown in TableIII-2.

Comparative Example III-1

[0138] As a retention aid, an aqueous solution was used which contains a0.05 mass % of a cationic acrylic polymer (a copolymer of DAC:AM=10/90(molar ratio), 0.5% salted viscosity=70 mPa·s, paste form product). Theretention aid was produced as follows: the cation A was added to waterunder stirring, and it took 180 minutes to completely dissolve thecation A. This is referred to as the retention aid cation A.

[0139] Performances of the retention aid were evaluated in the samemanner as in Example III-1, except that the cation A was used in 250 ppm(solid content, in relation to pulp). The results obtained are shown inTable III-2. TABLE III-1 Average ratio between Amphoteric the mixedconstituent Retention polymers monomers (molar Ca/An after aid (parts)ratio) mixing BL-4 CR-1 AR-1 DAC/AA/AMD 2.57 (70) (30) (38/15/47) BL-5CR-4 AR-1 DAC/AA/AMD 2.39 (60) (40) (46/19/35)

[0140] TABLE III-2 Retention aid (ppm) Second First addition additionTotal BL-4 BL-5 AR-1 Cation A CR-1 retention (%) Example 250 — — — —86.6 III-1 Example — 250 — — — 87.1 III-2 Example — — 75 — 175 87.2III-3 Comparative — — — 250 — 84.1 example III-1

[0141] Industrial Applicability

[0142] When the composition of the present invention is used as anamphoteric polymer flocculant, the composition is excellent in variousflocculation and dewatering performances in such a way that thefiltration rate is fast for various types of sludge, in particular, forsludge high in ratio of excess sludge, and the obtained flocs are largein diameter and excellent in self-supportability and peelability.Additionally, the composition of the present invention, as a retentionaid, can achieve process yield improvement in papermaking process.

1. A composition which comprises amphoteric polymers comprising, asconstituent monomer units, a cationic monomer unit, an anionic monomerunit, and optionally a nonionic monomer unit and having a 0.5% saltedviscosity of 10 to 120 mPa·s, wherein said amphoteric polymers comprisea first amphoteric polymer satisfying the following expression (1), anda second amphoteric polymer satisfying the following expression (2) or athird amphoteric polymer satisfying the following expressions (3) and(4): Ca₁/An₁≧1  (1) Ca₂/An₂<1  (2) Ca₃/An₃≧1  (3)|(Ca₁−An₁)−(Ca₃−An₃)|≧1.5  (4) wherein Ca₁ and An₁ respectivelyrepresent the total mole number of the cationic monomer units and thetotal mole number of the anionic monomer units in the first amphotericpolymer on a condition that the total mole number of all the constituentmonomer units in the first amphoteric polymer is converted to be 100mol; on a condition similar to the above, Ca₂ and An₂ respectivelyrepresent the total mole number of the cationic monomer units and thetotal mole number of the anionic monomer units in the second amphotericpolymer; and on a condition similar to the above, Ca₃ and An₃respectively represent the total mole number of the cationic monomerunits and the total mole number of the anionic monomer units in thethird amphoteric polymer.
 2. A composition according to claim 1,comprising, as amphoteric polymers, the first amphoteric polymer and thesecond amphoteric polymer.
 3. A composition according to claim 1,comprising, as amphoteric polymers, the first amphoteric polymer and thethird amphoteric polymer, wherein said amphoteric polymers each containsa cationic monomer unit, an anionic monomer unit and a nonionic monomerunit as indispensable constituent monomer units, and proportion of thenonionic monomer units to all the constituent monomer units in all theamphoteric polymers of the composition is 60 mol % or more.
 4. Anamphoteric polymer flocculant comprising the composition according toclaim
 1. 5. An amphoteric polymer flocculant according to claim 4,comprising, as amphoteric polymers, the first amphoteric polymer and thesecond amphoteric polymer.
 6. An amphoteric polymer flocculant accordingto claim 4, comprising, as amphoteric polymers, the first amphotericpolymer and the third-amphoteric polymer, wherein said amphotericpolymers each contains a cationic monomer unit, an anionic monomer unitand a nonionic monomer unit as indispensable constituent monomer units,and proportion of the nonionic monomer units to all the constituentmonomer units in all the amphoteric polymers of the composition is 60mol % or more.
 7. A sludge dewatering method, in which the amphotericpolymer flocculant according to claim 4 is added to sludge, and thendewatering is made.
 8. A sludge dewatering method according to claim 7,wherein said amphoteric polymers comprises the first amphoteric polymerand the second amphoteric polymer.
 9. A sludge dewatering methodaccording to claim 7, wherein said amphoteric polymers comprises thefirst amphoteric polymer and the third amphoteric polymer, wherein saidamphoteric polymers each contains a cationic monomer unit, an anionicmonomer unit and a nonionic monomer unit as indispensable constituentmonomer units, and proportion of the nonionic monomer units to all theconstituent monomer units in all the amphoteric polymers of thecomposition is 60 mol % or more.
 10. A sludge dewatering methodaccording to claim 8, in which an anionic polymer flocculant is furtheremployed.
 11. A sludge dewatering method according to claim 10, whereinsaid anionic polymer flocculant comprises a copolymer in whichcopolymerization ratio of anionic monomer units is 30 mol % or more. 12.A sludge dewatering method according to claim 9, in which an anionicpolymer flocculant is further employed.
 13. A sludge dewatering methodaccording to claim 12, wherein said anionic polymer flocculant comprisesa copolymer in which copolymerization ratio of anionic monomer units is5 mol % or more.
 14. A sludge dewatering method according to claim 7,wherein polymer flocculants are added to sludge in such a way that aratio of the total sum of the cationic monomer units to the total sum ofthe anionic monomer units in all the added polymer flocculants satisfiesthe following expression (5). 0.3≦Ca_(all)/An_(all)≦10  (5) wherein, inthe above expression (5), Ca_(all) and An_(all) respectively representthe total mole number of all the cationic monomer units and the totalmole number of all the anionic monomer units on a condition that the sumof the total amount of all the cationic monomer units and the totalamount of all the anionic monomer units, in all the added polymerflocculants, is converted to be 100 mol.
 15. A sludge dewatering methodaccording to any one of claims 8, 10 and 11, wherein polymer flocculantsare added to sludge in such a way that a ratio of the total sum of thecationic monomer units to the total sum of the anionic monomer units inall the added polymer flocculants satisfies the following expression(5-1). 0.3≦Ca_(all)/An_(all)≦4.0  (5-1) wherein, in the above expression(5-1), Ca_(all) and An_(all) respectively represent the total molenumber of all the cationic monomer units and the total mole number ofall the anionic monomer units on a condition that the sum of the totalamount of all the cationic monomer units and the total amount of all theanionic monomer units, in all the added polymer flocculants, isconverted to be 100 mol.
 16. A sludge dewatering method according to anyone of claims 9, 12 and 13, wherein polymer flocculants are added tosludge in such a way that a ratio of the total sum of the cationicmonomer units to the total sum of the anionic monomer units in all theadded polymer flocculants satisfies the following expression (5-2).0.5≦Ca_(all)/An_(all)≦10  (5-2) wherein, in the above expression (5-2),Ca_(all) and An_(all) respectively represent the total mole number ofall the cationic monomer units and the total mole number of all theanionic monomer units on a condition that the sum of the total amount ofall the cationic monomer units and the total amount of all the anionicmonomer units, in all the added polymer flocculants, is converted to be100 mol.
 17. A retention aid for use in papermaking, comprising thecomposition according to claim
 2. 18. A papermaking method wherein theretention aid according to claim 17 is added to stuff, and thenpapermaking is made.
 19. A method according to claim 18, wherein theretention aid is added in such a way that a ratio of the total sum ofthe cationic monomer units to the total sum of the anionic monomer unitsin all the added retention aids satisfies the following expression(5-1). 0.3≦Ca_(all)/An_(all)≦4.0  (5-1) wherein, in the above expression(5-1), Ca_(all) and An_(all) respectively represent the total molenumber of all the cationic monomer units and the total mole number ofall the anionic monomer units on a condition that the sum of the totalamount of all the cationic monomer units and the total amount of all theanionic monomer units, in all the added retention aids, is converted tobe 100 mol.